The effects of data quality in local earthquake tomography: Application to the Alpine region

Despite the increase in quality and number of seismic stations in many parts of the world, accurate timing of individual arrival times remains crucial for many tomographic applications. To achieve a data set of high quality, arrival times need to be picked with high accuracy, including a proper assessment of the uncertainty of timing and phase identification, and a high level of consistency. We have investigated the effects of data quantity and quality on the solution quality in local earthquake tomography. We have compared tomographic results obtained with synthetic and real data of two very different data sets. The first data set consisted of a large set of arrival times of low precision and unknown accuracy taken from the International Seismological Centre (ISC) Bulletin for the greater Alpine region. The second high-quality data set for the same region was seven times smaller and was obtained by automated quality-weighted repicking. During a first series of inversions, synthetic data resembling the two data sets were inverted with the same amount of Gaussian distributed noise added. Subsequently, during a second series of inversions, the noise level was increased successively for ISC data to study the effect of larger Gaussian distributed error on the solution quality. Finally, the real data for both data sets were inverted. These investigations showed that, for Gaussian distributed error, a smaller data set of high quality could achieve a similar or better solution quality than a data set seven times larger but about four times lower in quality. Our results further suggest that the quality of the ISC Bulletin is degraded significantly by inconsistencies, strongly limiting the use of this large data set for local earthquake tomography studies.

[1]  D. Giardini,et al.  Automatic seismic phase picking and consistent observation error assessment: application to the Italian seismicity , 2006 .

[2]  Roel Snieder,et al.  Bias in reported seismic arrival times deduced from the ISC Bulletin , 1999 .

[3]  E. Kissling,et al.  Investigating effects of 3-D ray tracing methods in local earthquake tomography , 2001 .

[4]  D. Giardini,et al.  Dynamic of retreating trench: insight from laboratory experiments , 2003 .

[5]  E. Kissling,et al.  Model parametrization in seismic tomography: a choice of consequence for the solution quality , 2001 .

[6]  C. Thurber,et al.  Theory and Observations – Seismic Tomography and Inverse Methods , 2007 .

[7]  E. Papadimitriou,et al.  3D crustal structure from local earthquake tomography around the Gulf of Arta (Ionian region, NW Greece) , 1999 .

[8]  D. Eberhart‐Phillips,et al.  Three-dimensional velocity structure in northern California Coast Ranges from inversion of local earthquake arrival times , 1986 .

[9]  Clifford H. Thurber,et al.  A fast algorithm for two-point seismic ray tracing , 1987 .

[10]  Urs Kradolfer,et al.  Initial reference models in local earthquake tomography , 1994 .

[11]  E. R. Engdahl,et al.  Evidence for deep mantle circulation from global tomography , 1997, Nature.

[12]  Stephen P. Grand,et al.  A possible station bias in travel time measurements reported to ISC , 1990 .

[13]  J. Trampert,et al.  Effects of arrival time errors on traveltime tomography , 2000 .

[14]  Ernst R. Flueh,et al.  Local earthquake tomography of shallow subduction in north Chile: A combined onshore and offshore study , 2000 .

[15]  Felix Waldhauser,et al.  Three dimensional interface modelling with two-dimensional seismic data: the Alpine crust-mantle boundary , 1998 .

[16]  G. Schubert,et al.  Treatise on geophysics , 2007 .

[17]  Stefan Wiemer,et al.  Probabilistic earthquake location in complex three‐dimensional velocity models: Application to Switzerland , 2003 .

[18]  Clifford H. Thurber,et al.  Earthquake locations and three‐dimensional crustal structure in the Coyote Lake Area, central California , 1983 .

[19]  Robert D. van der Hilst,et al.  Travel-time tomography of the European-Mediterranean mantle down to 1400 km , 1993 .

[20]  R. Caby,et al.  Fission-track evidence for Late Triassic oceanic crust in the French Occidental Alps , 1984 .

[21]  A. Michael,et al.  Three‐dimensional velocity structure, seismicity, and fault structure in the Parkfield Region, central California , 1993 .

[22]  D. Eberhart‐Phillips,et al.  Continental subduction and three‐dimensional crustal structure: The northern South Island, New Zealand , 1997 .

[23]  Tobias Diehl,et al.  Consistent phase picking for regional tomography models: application to the greater Alpine region , 2009 .

[24]  Edi Kissling,et al.  Geotomography with local earthquake data , 1988 .

[25]  Olafur Gudmundsson,et al.  Stochastic analysis of global traveltime data: mantle heterogeneity and random errors in the ISC data , 1990 .

[26]  A. Douglas,et al.  On the onset of P seismograms , 1997 .

[27]  D. Giardini,et al.  Moho depth and Poisson's ratio in the Western-Central Alps from receiver functions , 2008 .